Mobile telephones equipped with a GPS receiver have become widespread globally in recent years. There is a need to reduce the number of component parts and lower the cost of such mobile telephones. From the standpoint of system configuration, the GPS signal frequency and the frequency of the mobile telephone have different reference frequencies and the conventional practice is to equip a single mobile telephone with two reference signal oscillators (such as a TCXO). Generally, a reference signal oscillator is high in cost and hence there is strong demand for a system that operates with a single reference oscillator.
Patent Document 1 discloses a frequency synthesizer for dealing with this demand. The frequency synthesizer described in Patent Document 1 comprises a first frequency synthesizer subunit for converting a reference frequency signal to a signal of a frequency band of a first type; a second frequency synthesizer subunit for converting the reference frequency signal to a signal of a frequency band of a second type and an intermediate frequency signal; and a third frequency synthesizer subunit for converting the reference frequency signal to an auxiliary signal of a fixed frequency, wherein the auxiliary signal is used together with the intermediate frequency signal in generating signals of frequency bands of third and fourth types. Further, the first to third frequency synthesizer subunits each have a phase-locked loop frequency synthesizer for generating an integrally multiplied signal by integrally multiplying a frequency-divided signal.
[Patent Document 1]
Japanese Patent Kokai Publication No. JP2003-198366A